The present invention relates to a wave power station for conversion and storage of wave energy.
Wave energy, also termed blue energy, constitutes a substantially unexploited energy source for extraction of environmentally friendly and renewable energy in the form of electric power. Extraction of energy from sea waves via wave power stations is the method which has greatest potential compared with other methods based on tidal differences, temperature differences or differences in salt water concentration. Sea waves contain 15-20 times more energy per square meter compared with wind and sun. According to the IEA, the global potential for wave energy is between 8,000 and 80,000 TWh. By utilizing a small part of the potentially available wave energy, the switch from present-day fossile-based power production to an environmentally friendly renewable electric power production based on wave energy, can be strongly accelerated.
Problems which must be borne in mind in the design of a wave power station include wear and tear or damage which can occur due to flowing water and corrosive environment, or due to collision with ships, etc. Even if the environmental consequences of a wave power station for the environment are considered small, possible negative effects on the marine systems must be borne in mind. A further problem which should be borne in mind is the high investment costs.
According to recently published British compilations, the cost, today, of a full-scale prototype lies at between 70,000 and 100,000 Swedish Kr/kW. A 10 MW wave power farm is deemed to cost between 500-600 million (50,000-60,000 Kr/kW) according to the same source.
A few different types of wave power stations exist, e.g. wave power stations based on so-called oscillating water cylinders (OWC). An OWC is an air reservoir, usually a vertically upright cylinder, which is open on the bottom side toward the water surface and which has an air outlet via a turbine on the top side of the cylinder. When a wave strikes the cylinder, the water level in the cylinder rises, whereupon air inside the cylinder is compressed so that the air pressure drives the turbine.
Another common type of wave power station is based on the coupling together of many floating bodies, so-called multisegment structures, which are arranged at right angles to incoming waves. The floating bodies are coupled together via articulated joints, which allow the floating bodies to move relative to one another. The relative movements of the floating bodies, which movements are concentrated in the articulated joints between the floating bodies, are utilized for the pressurization of hydraulic pistons, which drive a fluid through a motor, which in turn drives an electric generator.
A third type of wave power station utilizes the energy in up and down movements in a floating body through the use of an arrangement of drive lines coupled between the floating body and an anchorage point and/or a counterweight via one or more power generating arrangements, e.g. electric generators for production of electric current.
In patent document US 2014152015 A1, FIG. 1, a wave power station of the last-named type is described. The wave power station 10, FIG. 1, comprises an energy absorbing unit 100, an energy accumulating unit 200 and a power generating unit 300, arranged in a surface-based floating body 20. Via a drive line 32, and a rotor drum 120 in the energy absorbing unit 100, the surface-based floating body 20 is connected to a bottom foundation 30, alternatively to an anchoring buoy 30a, 30b.
Via a second drive line 42 and a second rotor drum 40 in the power accumulating unit 200, the surface-based floating body 20 is also connected to a counterweight 40. The driving of the two power generating rotor drums 120,230 is determined by the up and down movement of the floating body 10 relative to the bottom foundation 30 and relative to the counterweight 40.
One problem with said wave power station is the large inertia of the floating body, which implies low or zero degree of utilization of the wave power station in case of low wave height.
A further problem is the arrangement of drive lines between the two power generating rotor drums 120, 230 and the bottom foundation 30 or the counterweight 40, which makes the wave power station complex.
A further problem is that the wave power station has no facility for intermediate storage of energy in order to even out variations in wave height/wave intensity.
It is desirable to provide a wave power station having a high degree of utilization even in case of small to medium-high wave height/wave intensity.
It is also desirable to provide:
a wave power station having a facility for intermediate storage of wave energy/power so as to even out variations in the power production in case of variations in wave height/wave intensity,
a single wave power station having few moving parts, which can be easily maintained,
a wave power station which can be easily coupled together with other wave power stations to form larger wave power systems,
a wave power station adapted to harsh environments, incl. corrosion from seawater.
Thus, according to an aspect of the present invention, a wave power station having a high degree of utilization in case of small to medium-size waves, for conversion and storage of wave energy from a water system, for example oceans, seas, rivers, has been provided.
According to a first preferred embodiment of an aspect of the invention, the wave power station comprises: an energy absorbing unit comprising a first floating body connected to a vertically hanging counterweight via a drive line and a drive wheel, a power generating unit comprising at least one power generation unit, for conversion of wave energy, connected to a drive shaft, and a power accumulating unit comprising at least one power accumulator for storage of converted wave energy, wherein the power generating unit and the power accumulating unit are arranged in a central cavity in a toroidal second floating body firmly anchored under the first floating body, wherein the drive line is connected to said at least one power generation unit via the drive wheel and a coupling and transmission unit arranged on the drive shaft for driving of said at least one power generation unit, wherein said at least one power generation unit comprises two opposite-acting electric generators, with opposite direction of rotation relative to each other, arranged on the drive shaft, for alternate generation of electric current via the up and down movements of the drive line in time with the wave movements, wherein the drive shaft, the drive wheel, the switching and transmission unit, said at least one power generation unit and said at least one power accumulator are arranged in a container in the central cavity of the toroidal second floating body, and wherein said at least one power accumulator comprises at least two chargeable battery cells for storage of electric current from the two opposite-acting electric generators.
Further preferred embodiments are defined below:
According to a second preferred embodiment, the drive shaft, the coupling and transmission unit and the drive wheel are arranged in a bearing housing, fixedly mounted in the container.
According to a third preferred embodiment, the container is loosely arranged and rests on a seat disposed on the lower part of the inner envelope surface of the central cavity, via a flange on the lower end of the container.
According to a fourth preferred embodiment, said at least one power generation unit comprises two opposite-acting compression pumps for compression of air.
According to a fifth preferred embodiment, said at least one power accumulator comprises three outer pressure vessels for storage of compressed air, wherein the three outer pressure vessels are arranged in the toroidal part of the second floating body.
According to a sixth preferred embodiment, the three outer pressure vessels comprise watertight elastic inner pressure vessels for storage of the compressed air.
According to a seventh preferred embodiment, the three outer pressure vessels are separated from one another by three floating containers, comprising floating elements, comprising cellular plastic.
According to an eighth preferred embodiment, the drive line is rotatably mounted on the bottom side of the first floating body via a rotating coupling.
According to a ninth preferred embodiment, the second floating body is firmly anchored to a bottom foundation on the ocean bed or sea bed via at least one anchoring wire.
According to a tenth preferred embodiment, one end of the anchoring wire is fixedly arranged on a first point of attachment on the bottom side of the second floating body, and the other end is detachably arranged on a second point of attachment disposed on the top side of the second floating body, wherein the anchoring wire runs from the first point of attachment to the second point of attachment via an eye bolt disposed on the concrete foundation and via a guide hole in one of the floating containers.
The invention implies, according to aspects thereof, a number of advantages and effects, the most important of which are:
The wave power station has a high degree of utilization even in case of low to medium-high wave height/wave intensity, which means that the wave power station can be in operation the whole time, apart from when there is absolute calm.
The wave power station is of flexible and modular construction, which means:
that the number of power generating parts can be easily varied and exchanged,
that the wave power station can be easily coupled together with other wave power stations to form larger or smaller wave power station systems with regard to factors such as site access, electric power requirements and environment.
The design of the wave power station enables intermediate storage of wave energy in case of variations in wave height/intensity, for example in the form of electric current in chargeable batteries or in the form of compressed air in pressure vessels.
The wave power station comprises no parts above water level which can damage animal life, cause noise or otherwise be disturbing, or pose a risk to activities on the water surface.
The wave power station is maintenance-friendly, since no underwater or high-level works are required. Maintenance works are carried out on the water surface, in that the anchorage of the wave power station to a bottom foundation can be released, whereupon the wave power station is hoisted to sea level under controlled conditions. The wave power station can thereby, indeed, be easily moved or scrapped on the day this becomes an issue.
The wave power station is in principle independent of sea depth, which means that the wave power station can be placed where wave conditions are best.